Graphs with Maximum Generalized Complementary Second Zagreb Index

In this paper, we confirm a conjecture by Furtula and Oz regarding graphs that maximize the second complementary Zagreb index. We demonstrate that this conjecture holds for a broader class of indices, each of which is parameter-dependent, and which we will refer to as the generalized complementary second Zagreb index. It is shown that all indices in this class are maximized by complete split graphs. Additionally, we analyze the behavior of the clique order in optimal graphs. For the case of the second complementary Zagreb index, we provide an explicit expression, thereby confirming the value conjectured by Furtula and Oz.